The invention relates to stabilized amido acid compositions. More particularly, the invention relates to compositions of amido acids, such as 6-nonanoylamidohexanoic acid, stabilized with antioxidants. The stabilized amido acid compositions are useful in the manufacture of bleach activators such as sodium nonanamidohexanoyloxybenzenesulfonate. Stablization of the amido acid protects chemical degradation. Additionally, bleach activators made from the stabilized amido acids of the invention possess improved color.
Hypochlorite and hydrogen peroxide are well known for their bleaching properties. As a bleaching agent in laundry detergents, hydrogen peroxide has the advantage of being safe to use with many fabric dyes. However, hydrogen peroxide bleaches are not effective at temperatures below 50xc2x0 C. This limits their use as most laundering is carried out at temperatures below about 40xc2x0 C. For this reason, various peroxyacids were developed as alternative bleaching agents for use in laundry detergents. The peroxyacids were generally found to be effective bleaching agents at the lower laundering temperatures. Because of their chemical instability and potential safety hazards, however, peroxyacids themselves are generally unsuitable for storage and handling.
Bleach activators were developed to address storage and handling concerns associated with peroxyacids. Bleach activators have the ability to hydrolyze under laundering conditions, effectively producing peroxyacids, even at lower temperatures, e.g. below 40xc2x0 C. By perhydrolyzing bleach molecules, bleach activators enhance the activity, and thus the cleaning ability, of a laundry detergent. Bleach activators have the further advantage of being stable when stored in solid form at room temperature. These properties permit the use of bleach activators in a wide variety of laundry detergents and other cleaning formulations.
An important class of bleach activators is phenyl ester salts. An effective bleach activator, phenyl ester salts readily react with bleach to form the corresponding peroxyacid. Exemplary phenyl ester salts, which are used as bleach activators, and their preparation are described in U.S. Pat. Nos. 4,634,551; 4,852,989; 5,391,780; 5,393,905; 5,393,901; 5,414,099; 5,466,840; 5,523,434; 5,650,527; and 5,717,118; as well as in published PCT applications WO 94/18159, WO 95/07883, WO 96/16148, and WO 99/09004. These U.S. Patents and published PCT applications are incorporated herein in their entirety.
Bleach activating phenyl ester salts can be prepared in various ways. For example, sodium nonanamido-hexanoyloxybenzenesulfonate can be prepared by reacting a Cg fatty acid, and caprolactam to form 6-nonanoylamidohexanoic acid. Sodium p-hydroxy-benzenesulfonate and acetic anhydride are then reacted with the nonanoylamidohexanoic acid (an amido acid) in a solvent to form sodium nonanamidohexanoyloxybenzenesulfonate. This reaction mechanism is shown below in equations 1A and 1B. 
The major difficulty with such a reaction is the formation of unwanted colored by-products. As such, the final product can possess a commercially undesirable non-white appearance. The formation of these non-white, colored by-products are believed to be due in large part to the oxidation of the amido acid intermediate formed during the process. Such an oxidation process may be similar to the oxidation of N-alkylamides, as described by Sager: M. V. Lock and B. F. Sager, J. Chem. Soc. (B), (1966), 690, B. F. Sager, J. Chem. Soc. (B), (1967), 428, and B. F. Sager, J. Chem. Soc. (B), (1967), 1047. Oxidation of the amido acid intermediate causes the formation of unwanted color as well as chemical degradation of the amido acidxe2x80x94both of which are undesirable.
The removal of unwanted colored by-products from the commercial phenyl ester salts is difficult and expensive. Indeed, current techniques for removing color from phenyl ester salts, such as sodium nonanamidohexanoyloxybenzenesulfonate, either fail to produce a colorless, commercially desirable, white product or require undue time and/or expense. For example, one technique used in forming amido acid phenyl esters involves sparging an inert gas through the amido acid reaction system. See, for example, U.S. Pat. No. 5,414,099. Another technique which has been described involves admixing a water-based purification system with an amido acid phenyl ester sulfonate reaction product to form a purification system and separating the purified phenyl ester salt from the purification system such that a percentage of the color forming impurities are removed. See, for example, published PCT Application WO 99/09004.
Accordingly, there is a need in the art for a simple, cost-effective means of forming precluding or lessening the formation of colored by-products during the synthesis of phenyl ester salts.
The invention answers the problems connected with forming substantially discoloration-free phenyl ester salts, which may be used as bleach activators. More particularly, commercially acceptable amido acids for use in the formation of bleach activating phenyl ester salts generally appear white and do not contain discolored amido acid by-products. By employing white amido acid products in the preparation of phenyl ester salts, a commercially acceptable phenyl ester salt can be prepared.
The invention aids in the prevention of discoloration and chemical degradation by providing stabilized liquid amido acid compositions. More specifically, the invention provides a stabilized liquid amido acid composition which contain at least one amido acid and an antioxidant. Additionally, the invention relates to processes of making a stabilized amido acid composition as well as processes for preparing an amido phenyl ester salt from an antioxidant stabilized amido acid.
According to the invention, amido acids can be stabilized to prevent or reduce their discoloration and chemical degradation. These stabilized amido acids are useful in the preparation of bleach activating, phenyl ester salts by processes known in the art. Simply put, the invention combines an antioxidant with an amido acid, typically a amido-carboxylic acid to form a stabilized amido acid. These stabilized amido acids may be used in the preparation of bleach activating amido phenyl ester salts which may be used in laundry detergents, fabric softeners, hard surface cleaners and other bleach-containing cleaning compositions.
Generally, discolored amido acid by-products and chemical degradation result from the absorption of oxygen by an amido acid product. The amido acid is particularly susceptible as a melt or in solution. To avoid the absorption of oxygen into a liquid amido acid product, an effective stabilizing amount of an antioxidant is added to an amido acid product. The presence of the antioxidant prevents or reduces the absorption of the oxygen such that the product does not become visibly discolored, e.g., a yellow or brownish coloration, or does not chemically degrade.
Amido Acids
The amido acids that can be stabilized through the use of the invention include amido-carboxylic acids. Exemplary amido-carboxylic acids include those represented by formulas I and II: 
where R1 is selected from C1-C22 alkyl, C2-C22 alkenyl, C2-C22 alkynyl, C3-C22 cycloalkyl, and C6-C14 aryl; R2 and R5 are each independently selected from hydrogen, C1-C22 alkyl, C2-C22 alkenyl, C2-C22 alkynyl, C3-C22 cycloalkyl, C6-C14 aryl, and where in formula II, R2 and R5 can together with the nitrogen carrying them form a C3-C10 heterocycle; R3 and R4 are each independently selected from hydrogen, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C3-C10 cycloalkyl, C6-C10 aryl and where R3 and R4 may together with the carbon carrying them form a C3-C10 cycloalkyl; and n is an integer from 0 to 20. The phrase xe2x80x9cindependently selectedxe2x80x9d means that the various radicals may or may not be the same. This phrase also means that when n is greater than 1, each CR3R4 group may or may not be the same.
Preferably, the individual substituents for the amido-carboxylic acids of formulas I and II are as follows: R1 is selected from C5-C15 alkyl, C5-C15 alkenyl, C5-C15 alkynyl, C5-C15 cycloalkyl, and C6-C14 aryl; R2 and R5 are each independently selected from hydrogen, C5-C15 alkyl; R3 and R4 are each independently selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C6 cycloalkyl, C6-C10 aryl and where R3 and R4 together with the carbon carrying them form a C3-C6 cycloalkyl; and
n is an integer from 0 to 10.
More preferably the individual substituents for the amido-carboxylic acids of formulas I and II are as follows: R1 is selected from C7-C11 alkyl; R2 and R5 are each independently selected from hydrogen and C7-C11 alkyl; R3 and R4 are each independently selected from hydrogen and C1-C5 alkyl n is an integer from 4 to 8. A particularly preferred amido acid is nonanamidohexanoic acid.
It is recognized that combinations of suitable, preferred and most preferred substituents can be used with the invention. For example, a preferred R1 could be used in conjunction with a suitable R2 and a most preferred R4.
Antioxidants
Any antioxidant or mixture of antioxidants capable of stabilizing the amido acids may be employed in the invention. Examples of preferred antioxidants include, but are not limited to, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene (sold under the product name Ethanox 330(copyright) from the Albemarle Corporation), Tetrakis(methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methane (sold under the product name Irganox(copyright) by Ciba-Geigy), butylated hydroxytoluene (BHT), and mixtures thereof.
An effective amount of an antioxidant for stabilizing the amido acid is any amount capable of preventing the oxidation of the amido acid. Preferably the antioxidant is present in an amount that will not affect the preparation of a bleach activating phenyl ester salt or its properties. Typically, the antioxidant is present in the stabilized amido acid composition in an amount of up to 5 wt %, more preferably ranging from about 0.001 to about 2 wt % of the composition, more preferably about 0.01 to about 1 wt % and most preferably, about 0.01 to about 0.1 wt %.
Stabilized Amido Acid Compositions
Typically, the amido acids of the invention do not undergo oxidation when the amido acids are in a solid state. Yet, when the amido acids are in solution and/or are a liquid or molten state, the amido acids can become oxidized resulting in the formation of visibly discolored amido acid by-products. In contrast, the inventive stabilized amido acid compositions are those that do not become visibly discolored when placed in a liquid or molten state. The amido acid discoloration is determined under normal lighting conditions by the naked eye.
Generally, the stabilized amido acid compositions are stable to oxidation discoloration and/or chemical degradation at a temperature of about 100xc2x0 C. for approximately 70 minutes. Preferably, the stabilized amido acid compositions do not become discolored when subjected to elevated temp for at least 120 minutes, more preferably 240 minutes and most preferably 72 hours or more. To determine whether the amido acid compositions are discolored, test samples of the amido acid compositions may be placed in tubes and then visually compared to colors of the platinum-cobalt scale contained in an adjacent tube.
The stabilized amido acid compositions can be in the form of a solid (typically crystalline), a melt or dissolved in a solvent. Although the stabilized amido acid can be stored as a solid, the stabilized amido acid is preferably stored as a liquid, e.g., a melt or a solution. A liquid form is preferred because it can be easily pumped to a reactor for conversion to a bleach activator. The use of solid, crystalline material is generally less preferred as the handling and continuous addition of a solid to a reaction process is more difficult than a liquid.
Process for Preparing Stabilized Compositions
The stabilized amido acid compositions of the invention may be formed by admixing the amido acids with an effective stabilizing amount of the antioxidant. The mixing of the two components may be accomplished by any conventional means. It is understood, however, that it is preferred that the amido acid is not subjected to temperatures far exceeding its melting point prior to its admixture with the antioxidant.
One suitable process for preparing the stabilized amido acid composition is to form a melt of the amido acid using a temperature slightly, 0-10xc2x0 C., above the melting point of the amido acid. To this amido acid melt is admixed a stabilizing effective amount of the antioxidant. Another suitable process involves forming a solution of the amido acid, such as a solution of amido acid and sulfolane, and admixing the antioxidant to the amido acid solution. Yet another process that may be used involves forming a particulate or powdered mixture of the amido acid and admixing the antioxidant to the powdered amido acid. This protects the compositions from discoloration or degradation upon melting or dissolving. The process of preparing the stabilized amido acid compositions may be performed either as a batch or continuous process.
Phenol Ester Salts formed from the Stabilized Compositions
The stabilized amido acid compositions of the invention may be used to form bleach activating phenyl ester salts. The preparation of these phenyl ester salts is discussed above. Phenyl ester salts prepared with the stabilized amido acid compositions of the invention are preferably substantially free of amido acid discoloring by-products. Any bleach activating phenyl ester salt that can be formed from an amido acid may also be prepared through the use of the inventive stabilized amido acids.
Bleach Activated Compositions Containing Phenyl Ester Salts
The phenyl ester salts prepared from the stabilized amido acids of the invention may be formulated into a wide variety of bleach activated compositions. Typically, the bleach activated phenyl ester salts of the invention are employed in the formation of laundry detergents and hard surface cleaners. Due to their ability to release hydrogen peroxide in an aqueous solution, however, the phenyl ester salts provide particular utility in laundry detergents for the bleaching of textiles. The bleach activating phenyl ester salts may be formulated into a wide range of detergent compositions. Suitable detergent compositions for the phenyl ester salts of the invention are described in Bums et al., U.S. Pat. No. 4,852,989, Bums et al., U.S. Pat. No. 4,634,551, Chapman et al., U.S. Pat. No. 5,534,194, Chapman et al., U.S. Pat. No. 5,534,195 and Guedira et al., WO 96/16148, herein incorporated by reference in their entirety.
The following examples are intended to illustrate, but not limit, the scope of the present invention.